For vehicle transportation, the dominant technology is hydrocarbon combustion to drive heat engines (internal combustion engines for cars, jet engines for planes, etc.). Other nascent transportation storage technologies include closed-cell batteries, fuel cells (e.g., H2 fuel cells), and longer-term possibilities for redox flow batteries for fast-refueling ground vehicles. These transportation technologies may suffer certain drawbacks that limit current or future applications: (a) fossil hydrocarbon combustion releases the greenhouse gas CO2, and biofuels (low net CO2) compete with food production, (b) gasoline cannot easily be “recharged” like a battery, (c) batteries are efficiently charged/discharged but are expensive, limited in energy density, and slow to recharge, (d) fuel cells are generally expensive, and (e) redox flow batteries are limited in energy density.